Conventionally, a semiconductor device has been fabricated by encapsulating various semiconductor elements such as transistor, IC and LSI with a ceramic package or the like, but in view of cost and mass productivity, resin encapsulation using a plastic package is recently predominating. In this type of resin encapsulation, an epoxy resin composition has been heretofore used and achieved good results.
However, technical innovation in the semiconductor field brings an increase in the integration degree and at the same time, drives large sizing of the element and miniaturization of the wiring, and the package also tends to become smaller and thinner. With this tendency, the encapsulating material is required to be more enhanced in reliability than ever. In recent years, to cope with requirement for more reduction in size and weight, the mode of package is transferring from QFP (Quad Flat Package) and SOP (Small Outline Package) to area-mounted package such as BGA (Ball Grid Array) including CSP (Chip Size Package) that is more respondent to multiple pins and allows for higher density mounting.
Meanwhile, the conventional package has a problem such as occurrence of separation between constituent members (mainly between an encapsulating resin and a die pad), which is attributable to a thermal stress generated between constituent members of a semiconductor device in the solder reflow step, and also in the recent single-sided resin encapsulation-type package, since the form thereof is single-sided encapsulation, deformation due to warpage in the solder reflow step is liable to occur, giving rise to a problem such as reduction in the mounting reliability. In order to solve this deformation problem attributable to warpage generation, irrespective of package configuration, it is greatly demanded to reduce the thermal stress generated due to difference in the linear expansion coefficient, modulus or the like between constituent members of the package, such as encapsulating resin and substrate.
The cause of generating warpage includes generation of a thermal stress due to (1) a large difference between the linear expansion coefficient of the substrate and the linear expansion coefficient of the encapsulating resin (that is, the linear expansion coefficient of the encapsulating resin is larger than that of the substrate) or (2) a large difference between the high-temperature modulus of the substrate and the high-temperature modulus of the encapsulating resin (that is, the high-temperature modulus of the encapsulating resin is larger than that of the substrate). Therefore, for reducing the linear expansion coefficient difference and the high-temperature modulus difference each responsible for generation of the thermal stress, studies are being made to increase the content of an inorganic filler in the encapsulating material (see, Patent Document 1).
Patent Document 1: JP-A-8-153831